In biotechnological, medical, technical and consumer applications, it is desirable to be able to link the physical product with digital information about the product. Such information could be common to a larger number of identical parts, such as manuals, ordering information, recycling information, or be related to the individual product, such as its manufacturing history or other relevant information about use of the product and be able to track the individual part during its use. Many such products are made by mass-replication techniques such as injection molding or extrusion coating, where each replication is similar and every part therefore practically indistinguishable from all other thus produced parts. It would be desirable to have a system where the molded parts may be encoded during molding without any additional processes, and be even more desirable in the case where each individual produced part could be easily identified and linked uniquely to its manufacturing conditions, use, age or other parameters important to the use or replacement of the part. It would be further desirable if this identification of each individual part would be fast and without the requirement of expensive and specialized equipment.
Molding of polymer parts is typically a fast process, where a replica is made of the mold once every few seconds or faster. If the above solution is to be industrially relevant for making unique codes, the change of the mold configuration should be executed within this time-frame. Furthermore, in most applications, no change of the macro-geometry is allowed.
To solve this problem, we have invented a method based on optical anisotropy, where the rotational state of a small area will change the reflectance in a given direction greatly, and may be determined by optical means, such as photography under simultaneous illumination.
The optically anisotropic surfaces are arranged in an array where each dot or bit in the array will define either a bright or dark state when illuminated and viewed from a given angle. In some embodiments, each of the areas of optically anisotropic surface may be individually rotated to alter the orientation of the optical anisotropy. Non-limiting examples of optically anisotropic surfaces are linear diffraction gratings, linear ridge gratings, oriented micro-reflectors or surfaces with a preferential direction of the surface roughness. By replication of these surfaces, the replica will obtain the same type of optical anisotropy as the master array.
These surfaces may be designed such that the perceived brightness for each individual element of the array will depend in a binary way (dark/bright) depending on the rotational orientation of the said element. The readout of the pattern may preferably be done by optical means, where the camera and the illuminating light source are placed close together, e.g. as in a smart-phone or a tablet.
The novelty and inventive step of the invention is realized by the surprisingly high contrast obtainable by optically anisotropic (surface) structures made on the surface of a single and homogeneous material, allowing detection thereof by consumer devices such as smartphones. Furthermore is the combination of a method where each mass-produced part is uniquely identifiable and a readout method using smartphones novel, and the possibility of using readily available devices with integrated data network capabilities, light source and camera, such as smartphones, makes this method industrially applicable, both for use in the industry and for consumers.